Say you are shortrowing, and you want to short row N stitches repeatedly (N being 2 or more)
When putting work into hold (reducing working needles), put N-1 needles into hold FURTHEST from the carriage, knit 1 row, put 1 needle into hold NEAREST the carriage, knit 1 row. Total after two passes = N, ie (N-1) + 1. Splitting N into N-1 and 1 means that the single HELD needle gets a wrap over it, which fills in the hole.
Shortrowing back out? Put N+1 needles furthest from the carriage into UWP, knit a row, put 1 needle nearest the carriage back into HOLD, knit a row. Total after two passes = N, ie (N+1) - 1
So, to shortrow 5 sts you'd put 4 sts into HOLD furthest from the carriage and knit 1 row, and then put 1 st into HOLD nearest to the carriage and knit 1 row (or however many rows are required).
When everything is in HOLD, you can either cancel it and continue, which will knit everything back into work, or you can short-row back out as follows:
Put 6 sts into UWP furthest from the carriage and knit a row, then put 1 st nearest the carriage back into HOLD and knit 1 row (or however many are required).
Clear as mud? It's the best I can do, and I still forget the principle sometimes.
Note: UWP = Upper Working Position, ie knit back from HOLD